Question

let f(x)=3x-2 and g(x)=x squared+6 use them (f-g)(x)

Answer 1

You don't often see the notation (f-g)(x)

I assume that it just means f(x) - g(x)
In your case, that would be
3x -2 -x^2 -6 = -x^2 +3x -8